PROJECT SUMMARY Project Description and Objectives: This project is responsive to the RFA mandate to examine the relationship between climate change and harmful algal blooms. The goal of Project 3 is to examine the role of natural attenuation in the context of the fate of extracellular secondary metabolites generated by harmful algal blooms and adjacent microbial communities. This is done with a focus to measuring the effects of climate change on the attenuation rate of microbial signals involved with quorum sensing; changes in harmful algal toxin expression (focusing on microcystins and anatoxin) as a function of algal culture exposure to the common multispecies signals autoinducer-2 and the acyl homoserine lactones, degradation of extracellular toxins in the water column and at sediments surfaces, and correlating the sedimentary record of buried toxins with past meteorological conditions. The kinetics and products of microbial signal degradation will be determined based on multifactorial environmental modeling experiments (including photochemical, hydrolytic and sediment- catalyzed processes). Harmful algal cultures will be interrogated for the presence of endogenous microbial signals, and their response to the addition of exogenous microbial signals will be determined, particularly focusing on the yield and type of toxin expressed. The kinetics and products of algal toxin degradation will be determined based on multifactorial environmental modeling experiments (including photochemical, hydrolytic and sediment-catalyzed processes). The concentration of microbial signals, toxins, and distinctive degradation products of both will be determined in natural water from Lake Waco, Waco TX with sampling sites chosen in consultation with Project 2. The concentration of harmful algal bloom toxins will also be determined in sediment cores dated using 210Pb. Initial core studies will focus on Lake Waco, enabling comparison of 210Pb, local meteorological records and historical records of algal blooms. Subsequent exploratory sediment analyses will be performed on cores withdrawn from a series of storm water retention ponds in SC that are known to have occasional harmful algal blooms but are not routinely monitored. The overall goal of this Project is to measure the environmental effects and persistence of extracellular metabolites critical to harmful algal blooms at both baseline conditions and those predicted as a result of climate change. 1